1. Field of the Invention
The present invention is generally related to an idle speed control system for an internal combustion engine and, more particularly, to a system that maintains the idle speed of an engine according to a predetermined plan which controls the engine speed as the function of the difference between a target speed or RPM and an actual speed of the boat or RPM of the engine, respectively.
2. Description of the Prior Art
Those skilled in the art of internal combustion engines are aware of many different types of speed control systems used to control the operation of the engine. For example, in automotive applications, the cruise control function has been available for many years. However, in marine propulsion systems, idle speed control is not generally available because the operating conditions relating to the use of a marine propulsion system are significantly different from automotive applications.
Unlike automotive applications of speed control systems, marine applications can experience variable conditions that operate to defeat the intent of maintaining a constant speed. For example, if the operating speed (RPM) of a marine engine is maintained at a constant magnitude, the marine vessel may experience changes in wind direction or water current direction which will change the boat speed even though the engine speed, measured in RPM, remains constant. Therefore, the relationship between boat speed and engine RPM in a marine application is not as generally predictable as in an automotive application.
The operator of a marine vessel occasionally desires to operate the vessel at a precise idle speed in order to fish in a manner that is commonly referred to as trolling. In trolling applications, the boat operator typically desires to maintain a constant boat speed regardless of wind direction and strength and regardless of the direction or strength of water currents. In order to maintain the constant boat speed, it may be necessary to frequently change the actual engine speed, measured in revolutions per minute.
U.S. Pat. No. 5,364,322 which issued to Fukui on Nov. 15, 1994, describes a control apparatus for a marine engine. The control apparatus is capable of effectively suppressing a great variation in the rotational speed of the engine due to a great variation in an intake air pressure particularly when the engine is trolling. In one form, an air/fuel ratio of a mixture supplied to the engine is made constant to maintain engine output power at a constant level. In another form, the intake air pressure, based on which the engine is controlled, is averaged in such a way as to reduce a variation in the engine rotational speed by using a greater averaging coefficient during trolling than at other times. In a further form, if a variation in the intake air pressure is less than a predetermined value, the intake air pressure is used controlling the engine, whereas if otherwise, another engine operating parameter such as an opening degree of a throttle valve is used instead of the intake air pressure.
U.S. Pat. No. 5,362,263 which issued to Petty on Nov. 8, 1994, describes a trolling autopilot for a vessel for use in combination with a depth finder having a transducer, including a means for setting and storing a desired characteristic to be followed by the vessel. It further includes means for measuring the characteristic to be followed by the vessel and means for storing a signal generated by the measuring means indicative of the measured characteristic. Once received and stored, the measured characteristic is compared to the selected characteristic. Based upon the comparison between the two characteristics, at least one servo motor is actuated to alter the direction the vessel is traveling. The servo motor may be coupled to the helm or to an outboard motor mounted to the vessel. The speed of the vessel may also be controlled based upon a comparison between a measured value and a selected value.
U.S. Pat. No. 5,070,803 which issued to Smith on Dec. 10, 1991, discloses a method and apparatus for reducing the trolling speed of boats having inboard engines. The apparatus for slowing the trolling speed of boats having a steerable rudder mounted under the stem of the boat aft of a propeller driven by the inboard engine includes a mechanical structure. The rudder has first and second opposed major sides and has first and second deflector plates carried on opposite sides of the rudder. The deflector plates are movable between the first, closed position wherein the first and second deflector plates reside closely adjacent to and substantially along the respective first and second major sides of the rudder and are substantially inoperative and a second, open position wherein the first and second deflector plates extend outwardly away from the opposed sides of the rudder into the wash from the propeller and are operative to create speed reducing drag to slow the forward movement of the boat.
U.S. Pat. No. 5,305,701, which issued to Wilson on Apr. 26, 1994, describes a device for controlling boat speed. The invention relates to attachments to the anticavitation plate of a boat motor for making and controlling small variations in boat speed below the normal motor idling speed to facilitate trolling for fish. The trolling speed control includes an incrementally adjustable unitary plate mounted for movement between a position fully across the normal paths of the propeller wash, thereby to slow the speed of the boat and to a fully retracted position out of the path of the propeller wash. This invention relates to a motorboat low speed control device.
In certain types of internal combustion engines which utilize homogenous combustible gaseous mixtures, it may also be necessary to provide a means for providing the internal combustion engine with an appropriate amount of air during operation at idle speeds. The amount of air provided to the internal combustion engine should be regulated in conformance with the amount of fuel provided to it. In the automotive field, this function is performed by idle air control devices.
U.S. Pat. No. 4,359,983, which issued to Carlson et al on Nov. 23, 1982, describes an engine idle air control valve with a position counter reset apparatus. A vehicle is driven by an internal combustion engine having an air induction passage with an idle air control valve positionable by a stepping motor in response to valve opening and valve closing pulses. A counter normally counts the pulses arithmetically to provide an indication of valve position. In order to bring the counter and valve position into accord, counter reset apparatus is effective, when actuated, to generate a predetermined number of valve closing pulses sufficient to stall the stepping motor against the stop, reset the counter to a predetermined reference count and generate a predetermined number of valve opening pulses to return the idle air return valve to a desired operating position with the counter counting such pulses in the normal manner. The apparatus is actuated upon the first occurrence of a vehicle speed greater than a predetermined speed such as 30 mph following a counter reset signal, which signal is generated upon each engine start and may further be generated at any time a counter error is detected. The minimum required vehicle speed guarantees that the engine will not stall during the period of the reset operation.
U.S. Pat. No. 4,337,742, which issued to Carlson et al on Jul. 6, 1982, describes an idle air control apparatus for an internal combustion engine. The apparatus for a vehicle driving internal combustion engine having an air induction passage includes a control valve in the air induction passage controlled by a stepper motor in response to the arithmetic count of applied electrical pulses, a register effective to store a valve control number representing the currently desired position of the control valve, apparatus effective upon occurrence of a predetermined engine loading event to change the valve control number in response thereto, an up-down counter effective to arithmetically count the pulses applied to the stepper motor and thus indicate actual control valve operation, a closed loop control effective to compare the contents of the up-down counter and register and apply pulses to the stepper motor at the first predetermined rate in order to reduce any difference therebetween and a speed trim loop active only during occurrence of a predetermined steady state idle condition to compare actual engine speed with the desired engine idle speed and arithmetically change the valve control number in the register at a second predetermined rate substantially slower than the first predetermined rate in order to reduce any difference between the speeds. Therefore, idle air control responds to large, sudden engine load changes and environmental factors to prevent engine stall but ignores small random speed fluctuations to maintain a stable engine idle speed.
U.S. patent application Ser. No. 08/939,829 (M09190) which was filed on Sep. 29, 1997 by Ehlers et al and assigned to the assignee of the present application, discloses an internal combustion engine with barometric pressure related start of air compensation for a fuel injector. The control system for a fuel injector system is provided with a method by which the magnitude of the start of air point for the injector system is modified according to the barometric pressure measured in a region surrounding the engine. This offset, or modification, of the start of air point adjusts the timing of the fuel injector system to suit different altitudes at which the engine may be operating.
The patents and patent application described above are hereby explicitly incorporated by reference in this description.
In view of the differences in operation between internal combustion engines used in automotive applications and those used in marine applications, it would be significantly beneficial if a control system could be developed which is able to maintain the boat speed at a constant magnitude regardless of the changing effects of wind and water currents.